For example, PTC heaters which are one form of electric heaters have a structure in which heat is generated by energizing a PTC element which is a resistive element having a positive temperature coefficient by a DC power supply. PTC heaters are widely used because a resistance thereof rapidly increases as temperature increases at a certain timing and thus a constant temperature can be maintained by simple energization from the DC power supply, leading to a simple control structure (for example, PTL 1). Conventionally, PTC heaters are driven so as to satisfy a required power by controlling ON and OFF of a plurality of switching elements corresponding to the PTC heaters based on predefined combination information in which combinations of ON and OFF states of the switching elements are associated with output powers provided by the combinations.